Tool for polishing glass, method for manufacturing glass-polishing tool, and method for polishing glass

ABSTRACT

A tool for polishing glass is formed by integrating multiple polishing elements in which polishing grains have been covered with a resin, and includes air cavities. The polishing grain volume S ratio is 50-85%, the resin volume ratio is 15-50%, the air cavity volume ratio is 20% or less, and the average grain size of the polishing elements is 10 μm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application based on a PCT Patent Application No. PCT/JP2020/025260, filed on Jun. 26, 2020, priority of which is claimed on Japanese Patent Application No. 2019-227565, filed on Dec. 17, 2019. The contents of both the PCT Application and the Japanese Application are incorporated herein by reference.

BACKGROUND Technical Field

The present invention relates to a polishing tool for optical glass, a method for manufacturing a glass-polishing tool, and a method for polishing optical glass.

Background Art

Conventionally, polishing tools with fine polishing grain diameters have been used for manufacturing parts for semiconductor manufacturing equipment or optical parts with high surface accuracy.

For example, Japanese Unexamined Patent Application, First Publication No. H11-207632 discloses a polishing tool of a mixture of polishing grains having an average grain size of 0.01-2.0 μm (micrometers) and resin particles having an average grain size of 0.1-20 μm. This polishing tool has a polishing grain volume ratio of 20-60%, a resin volume ratio (binder volume ratio) of 30-50%, and an air cavity volume ratio of 40% or less.

When polishing optical glass like a soft glass material such as S-FPL51, if the polishing grains in the polishing tool are too large, or if the polishing grains in the resin are poorly dispersed and the density is uneven, the optical glass is easily scratched. Further, if the polishing grains are too small, when polishing S-FPL51, S-LAH-based glass material, or the like, the polishing grains and resin that have fallen off may adhere to the surface of the optical glass, or the polishing tool may be affected by polishing resistance so as to easily degrade and have a short life.

SUMMARY

The present invention provides a tool for polishing glass, a method for manufacturing a glass-polishing tool, and a method for polishing optical glass, which are capable of polishing with good surface accuracy over a long period of time while suppressing the generation of scratches and adhered substances on the optical glass.

A tool for polishing glass (glass-polishing tool) is formed by integrating multiple polishing elements in which polishing grains have been covered with a resin, and includes air cavities, wherein the polishing grain volume ratio is 50-85%, the resin volume ratio is 15-50%, the air cavity volume ratio is 20% or less, and the average grain size of the polishing elements is 10 μm or less.

The average grain size of the polishing grains may be 0.4 μm or less, and the polydispersity index may be less than 0.25.

A method for manufacturing the tool for polishing glass includes: mixing the polishing grains and the resin to obtain a mixture, spray-drying the mixture to obtain a powder in which the polishing grains are coated with the resin, pulverizing the powder to obtain a molding powder having an average grain size of 10 μm or less, and pressurizing the molding powder under heating.

A method for polishing optical glass uses the tool for polishing glass and a processing liquid, wherein the zeta potential of the polishing grains and the zeta potential of the optical glass have the same sign, and the absolute value is 40 mV or more.

According to the tool for polishing glass, the method for manufacturing glass-polishing tool, and the method for polishing optical glass, it is possible to finish with good surface accuracy for a long period of time while suppressing the generation of scratches and adhered substances on the optical glass.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged schematic view of a polishing tool for optical glass according to a first embodiment of the present invention.

FIG. 2 is a flowchart of a method for manufacturing a polishing tool for optical glass according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a method for polishing optical glass according to a third embodiment of the present invention.

FIG. 4 is an image of a polished surface of the optical glass when the method for polishing optical glass according to the third embodiment is used.

FIG. 5 is an image of the polished surface of the optical glass when pure water is used instead of a processing liquid in the method for polishing optical glass according to the third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a first embodiment of the present invention will be described with reference to FIG. 1.

FIG. 1 is an enlarged schematic view of a polishing tool 10 for optical glass according to the first embodiment of the present invention. The polishing tool 10 is formed by integrating a large number of (a plurality of) polishing elements 11 coated with polishing grains 12 with resin 13. The polishing tool 10 has an air cavity 14. The air cavity 14 is, for example, a gap (space) generated when a plurality of spherical polishing elements 11 are integrated.

The polishing grains 12 can be formed of a material such as a compound of various metals or a compound of various minerals. As the material for forming the polishing grains 12, for example, cerium oxide or the like is suitable.

The resin 13 can be formed of various resin materials. As the material for forming the resin 13, for example, a phenol resin is suitable.

The average grain size of the polishing element 11 is preferably 10 μm or less. From the viewpoint of suppressing the generation of scratches and adhered substances on the optical glass, for example, it is more preferable that the average grain size of the polishing element 11 be in the range of 5-10 μm.

The ratio of the volume of the polishing grains 12 to the volume of the polishing tool 10 is defined as the “polishing grain volume ratio”. The polishing grain volume ratio is preferably in the range of 50-85%. It should be noted that the larger the polishing grain volume ratio, the greater the increase in the contribution to polishing by the polishing tool 10, so that the efficiency of polishing can be improved. From the viewpoint of improving the efficiency of polishing, for example, it is more preferable that the polishing grain volume ratio be in the range of 65-85%.

The ratio of the volume of the resin 13 to the volume of the polishing tool 10 is defined as the “resin volume ratio”. The resin volume ratio is preferably in the range of 15-50%. By setting the resin volume ratio to an appropriate value, it is possible to have an appropriate holding force for the polishing grains 12.

The ratio of the volume of the air cavity 14 to the volume of the polishing tool 10 is defined as the “air cavity volume ratio”. The air cavity volume ratio is preferably 20% or less.

It should be noted that the larger the air cavity volume ratio, the easier it is to peel off the polishing grains 12 worn by polishing. As a result, it is possible to promote a self-sustaining action of exposing the new polishing grains 12 on the surface of the polishing tool 10. From the viewpoint of promoting the self-sustaining action, for example, it is more preferable that the air cavity volume ratio be in the range of 10-20%.

The air cavity 14 is also a space for allowing the polishing grains 12 and the resin 13, which have been peeled off by polishing, to escape. The polishing tool 10 need not have an air cavity 14. For example, measures may be taken to provide a repulsive force between the surface of the optical glass and the polishing grains 12 and the resin 13 which have been peeled off.

In the polishing tool 10 configured as described above, the average grain size of the polishing material 11 is 10 μm or less.

According to this configuration, since the polishing element 11 is fine, it is possible to perform polishing with good surface accuracy for a long period of time while suppressing the generation of scratches and adhered substances on the optical glass.

In the present embodiment, a material other than cerium oxide may be used for the polishing grains 12. The material preferably used (material for forming the polishing grains 12) is, for example, zirconium oxide, aluminum oxide, silicon oxide, silicon carbide, calcium carbonate, sodium carbonate, or the like.

In the present embodiment, a material other than the phenol resin may be used for the resin 13. The material preferably used (material for forming the resin 13) is, for example, a thermosetting resin such as phenol, epoxy, melamine, polyurethane, and polyimide, a thermoplastic resin such as acrylonitrile, a copolymer of butadiene and styrene, polypropylene, polyethylene terephthalate, polyether imide, polystyrene, and the like.

In the present embodiment, the average grain size of the polishing grains 12 may be 0.4 μm or less, and the polydispersity index may be less than 0.25. According to this configuration, the grain size of the polishing grains 12 is small and uniform. For example, when polishing a highly soft glass material such as S-FPL53 or fluorite, it is possible to obtain good surface accuracy for a long period of time while suppressing the generation of scratches and adhered substances.

Next, a second embodiment of the present invention will be described with reference to FIG. 2. The second embodiment is a method for manufacturing the polishing tool for optical glass according to the first embodiment. FIG. 2 is a flowchart of a method 20 for manufacturing a polishing tool for optical glass according to a second embodiment of the present invention.

As shown in FIG. 2, in the method 20 for manufacturing a polishing tool for optical glass, first, the above-described polishing grains 12 (for example, cerium oxide) and resin 13 (for example, phenol resin) are prepared.

In step P1, the polishing grains 12 and the resin 13 dissolved in, for example, N-methyl-2-pyrrolidone are mixed to obtain a mixture in which the polishing grains 12 are dispersed in the resin 13.

Next, in step P2, the mixture in which the polishing grains 12 are dispersed in the resin 13 is dried by spray drying to obtain a powder in which the polishing grains 12 are coated with the resin 13.

Subsequently, in step P3, the powder is further pulverized and classified to obtain a molding powder having an average grain size of 10 μm or less.

Subsequently, in step P4, the molding powder is filled in a mold and pressed while heating to obtain a molded product having a predetermined shape.

Finally, in step P5, the molded body is sintered to obtain the polishing tool 10.

In the method 20 for manufacturing a polishing tool for optical glass having the above steps, by performing step P2 of spray-drying the mixture in which the polishing grains 12 are dispersed in the resin 13, the grain size of the polishing material 11 of the polishing tool 10 can be made fine, and the dispersion of the polishing grains 12 in the resin 13 can be made uniform. Further, by performing step P4 of heating at the time of molding, even if the polishing grains 12 are fine, the wear resistance of the polishing tool 10 can be improved and the life can be extended.

Next, a third embodiment of the present invention will be described with reference to FIG. 3. The third embodiment is a method for polishing optical glass using the polishing tool 10 of the first embodiment. FIG. 3 is a diagram showing a method 30 for polishing optical glass according to the third embodiment.

As shown in FIG. 3, the optical glass polishing method 30 is performed using a polishing tool 10, a rotary table 31, a holding device 15, a machining fluid injector 32, and a processing liquid 33.

The polishing tool 10 has a curved polishing surface P corresponding to a work surface S (surface) of an optical glass M.

The rotary table 31 can rotate around a first axis L (rotary axis) fixed in a fixed position. The rotary table 31 has a first surface T perpendicular to the first axis L.

The holding device 15 is rotatable around a second axis N (rotational axis) that can be translated and rotated. The holding device 15 has a second surface F perpendicular to the second axis N.

The machining fluid injector 32 has an injection port capable of injecting the processing liquid 33.

An optical glass polishing method 30 is performed in the following order.

First, the optical glass M is fixed to the first surface T of the rotary table 31, and the rotary table 31 is rotated around the first axis L. The optical glass M is, for example, S-FPL51, S-LAH-based glass material, or the like.

Next, the polishing tool 10 is fixed to the second surface F of the holding device 15, and the holding device 15 is rotated around the second axis N.

Subsequently, the machining fluid 33 is jetted from the injection port of the machining fluid injector 32 to hit the work surface S of the optical glass M. With the processing liquid 33, the zeta potential of the polishing grains 12 and the zeta potential of the optical glass M have the same sign, and the absolute value is 40 mV or more. The processing liquid 33 is, for example, an aqueous solution of sodium hexametaphosphate.

Subsequently, the optical glass M is polished by moving the holding device 15 to bring the work surface S of the optical glass M into contact with the polishing surface P of the polishing tool 10.

In the optical glass polishing method 30 having the above steps, the zeta potential of the polishing grains 12 and the zeta potential of the optical glass M have the same sign, and the absolute value is 40 mV or more. As a result, it is possible to prevent the surface of the optical glass M from being scratched. In addition, since a repulsive force is generated between the polishing grains 12 and the optical glass M, it is possible to suppress the fine polishing grains 12 and the resin 13, which have been peeled off from the polishing tool 10, adhering to the surface of the optical glass M.

In the present embodiment, an aqueous solution of a material other than sodium hexametaphosphate may be used as the processing liquid 33. The material preferably used (material used for the processing liquid 33) is, for example, various surfactants such as carboxylic acid-based surfactants, sodium pyrophosphate, sodium phosphate, and the like.

The present invention will be further described with reference to Examples and Comparative Examples. The technical scope of the present invention is not limited by the contents of Examples and Comparative Examples.

Example 1 is the optical glass polishing tool of the first embodiment manufactured by the method of manufacturing the optical glass polishing tool of the second embodiment. In Comparative Example 1 and Comparative Example 2, the air cavity volume ratio and the contents of the molding process are changed from those of Example 1.

Configuration of the Polishing Tool and the Manufacturing Method

Example 1 uses the following configuration.

Polishing grains

-   -   Material: Cerium oxide     -   Average grain size: 0.35 μm     -   Polydispersity index: 0.19

Resin material: Phenol resin

Volume ratio of polishing grains to resin: 3:1

Air cavity volume ratio: 16%

Average grain size of molding powder: 10 μm

Heating temperature: 150° C.

Pressure: 60 MPa (Megapascal)

Sintering temperature: 175° C.

Comparative Example 1 is different from Example 1 in that the heating temperature was set to 100° C. in the molding step and the air cavity volume ratio was 24%.

Comparative Example 2 is different from Example 1 in that heating was not performed in the molding process and the air cavity volume ratio was 25%.

Abrasion Resistance Evaluation

For Example 1, Comparative Example 1 and Comparative Example 2, S-FPL51 was continuously polished 10 times, and the amount of surface regression (μm) before and after processing was measured. Here, the amount of regression corresponds to the amount of wear on the surface of the optical glass after processing with respect to the surface before processing. The method for polishing optical glass according to the third embodiment was performed, and an aqueous solution of sodium hexametaphosphate (concentration 0.5 wt %) was used as the processing liquid.

The measurement results are shown in Table 1.

TABLE 1 SURFACE REGRESSION (μm) EXAMPLE 1 5 COMPARATIVE 8 EXAMPLE 1 COMPARATIVE 10 EXAMPLE 2

As shown in Table 1, when comparing Example 1 in which heating was performed in the molding process and Comparative Example 2 in which heating was not performed in the molding process, the amount of regression on the surface of the polishing tool was smaller in Example 1. As a result, it was confirmed that the wear resistance is enhanced by heating in the molding process.

Further, when comparing Example 1 and Comparative Example 1 in which heating was performed in the molding step, the amount of regression on the surface of the polishing tool was smaller in Example 1 having a smaller air cavity volume ratio. From this, it is considered that the regression amount and the air cavity volume ratio are related.

Polishing Quality Evaluation

Next, in the case where the optical glass polishing method of the third embodiment was performed using the optical glass polishing tool and the processing liquid of Example 1, and in the case where pure water was used instead of the processing liquid, the polished surface of the optical glass after polishing was observed. The optical glass to be polished was S-FPL51. As the processing liquid, 0.5 wt % aqueous solution of carboxylic acid-based surfactant was used. With this processing liquid, the zeta potential of the polishing grains became −75 mV, and the zeta potential of the optical glass became −55 mV, which had the same sign.

FIG. 4 is an image of the polished surface of the optical glass when the above-described optical glass polishing method was used (when a processing liquid was used). FIG. 5 is an image of the polished surface of the optical glass when pure water was used instead of the processing liquid in the method for polishing the optical glass.

As shown in FIG. 5, when pure water was used instead of the processing liquid, it was confirmed that scratches C and adhered matter A were generated on the polished surface of the optical glass.

On the other hand, as shown in FIG. 4, it was found that the generation of scratches C and adhered matter A on the polished surface of the optical glass can be suppressed by using the processing liquid.

Although the embodiments and examples of the present invention have been described above, the technical scope of the present invention is not limited to the above embodiments, and it is possible to change the combination of components, make various changes to each component, and delete them without departing from the spirit of the present invention. 

What is claimed is:
 1. A tool for polishing glass which is formed by integrating multiple polishing elements in which polishing grains have been covered with a resin, and comprises air cavities, wherein a polishing grain volume ratio is 50-85%, a resin volume ratio is 15-50%, an air cavity volume ratio is 20% or less, and an average grain size of the polishing elements is 10 μm or less.
 2. The tool according to claim 1, wherein an average grain size of the polishing grains is 0.4 μm or less, and a polydispersity index is less than 0.25.
 3. A method for manufacturing a glass-polishing tool, which is formed by integrating multiple polishing elements in which polishing grains have been covered with a resin and comprises air cavities, wherein a polishing grain volume ratio is 50-85 %, a resin volume ratio is 15-50%, an air cavity volume ratio is 20% or less, and an average grain size of the polishing elements is 10 μm or less, the method comprising: mixing the polishing grains and the resin to obtain a mixture, spray-drying the mixture to obtain a powder in which the polishing grains are coated with the resin, pulverizing the powder to obtain a molding powder having an average grain size of 10 μm or less, and pressurizing the molding powder under heating.
 4. A method for polishing optical glass using a glass-polishing tool and a processing liquid, the tool being formed by integrating multiple polishing elements in which polishing grains have been covered with a resin and comprising air cavities, wherein a polishing grain volume ratio is 50-85%, a resin volume ratio is 15-50%, an air cavity volume ratio is 20% or less, and an average grain size of the polishing elements is 10 μm or less, wherein a zeta potential of the polishing grains and a zeta potential of the optical glass have the same sign, and an absolute value is 40 mV or more. 